Electron-Impact Ionization Cross Sections for Silver

Absolute electron ionization cross sections have been measured for silver using a single-crossed-beam method. A silver beam was generated by vaporizing silver shot in a small high-temperature Knudsen cell, and passed through an ionization chamber where it intersected an electron beam at right angles. By applying suitable potentials to the chamber, ions could be accelerated either into a Faraday-cup total-ion collector, or into a large quadrupole mass spectrometer. After passing through the chamber, the silver beam was condensed in a weighable atomic-beam trap. Absolute cross sections were obtained by integrating the total-ion collector current, and calculating the silver beam intensity from the weight increase of the trap. The measured values at 75 eV are (4.65±1.0)×10−16cm2 for the formation of Ag+ and (4.75±3.0)×10−17cm2 for the formation of Ag++. The value for Ag+ agrees within experimental error with the extrapolated experimental values of other workers, but disagrees with theoretical predictions.